1. Field of the Invention
This invention relates to a cross-talk removal apparatus, which removes cross-talk from adjacent tracks contained in the reproduced signal of a main track based on reproduction signals from the main track and from both adjacent tracks of a data recording medium; and to a data reproduction apparatus that uses the cross-talk removal apparatus when reproducing data from a data-recording medium that has tracks.
2. Description of the Related Art
In the case of a large-capacity data-recording medium such as DVD, there is a problem in that cross-talk from adjacent tracks affects the reproduction signal from the main track being reproduced and causes the reproduction quality to decrease. In order to solve this problem, a cross-talk canceller has gained much attention, in which three light beams are used to simultaneously reproduce three adjacent tracks in order to obtain false cross-talk from the reproduction signals of the adjacent tracks, and then the cross-talk is removed by subtracting this cross-talk from the reproduction signal from the main track.
This kind of cross-talk canceller irradiates three light beams on the main track and both adjacent tracks and removes the cross-tack according to the respective reproduction signals. In order to do this, the cross-talk component is extracted by filtering the reproduction signals of the two adjacent tracks using a digital filter having a variable tap coefficient. This cross-talk canceller must adaptively control the aforementioned tap coefficient in order to follow changes in the cross-talk. This makes it possible to use an optimum tap coefficient to properly remove the cross-talk from the reproduction signal and to maintain the reproduction quality.
Recently, writable data-recording media such as DCD-RAM has become widely used. Normally, in the case of data-recording media such as DVD-RAM it is assumed that the recorded areas and non-recorded areas mixed together, so data are not necessarily recorded on the adjacent tracks when reproducing the data on the main track. When there are no data recorded on the adjacent tracks, there is no cross-talk between the adjacent tracks and the main track, however, when changing from having no data recorded on the adjacent tracks to having data recorded, cross-talk between the adjacent tracks and the main track occurs suddenly. In order to stably remove the cross-talk that corresponds to this kind of change, it is preferred that the tap coefficient of the cross-talk canceller be made to follow the change.
However, since the control frequency zone is somewhat narrow, control of the tap coefficient of the cross-talk canceller requires time in order to converge. Normally, the control frequency zone for the tap coefficient is set to be equal to or double the rpm of the disk. This is because when the control frequency zone for the tap coefficient is widened, the effects due to defects during reproduction are received, and there is a possibility that the cross-talk canceller will malfunction. Therefore, it is not possible to widen the control frequency zone for the tap coefficient and quickly change the characteristics of the cross-talk canceller even though the adjacent tracks changed from a state of having no data recorded to a state of having recorded data. As a result, it is not possible to sufficiently remove the cross-talk in the starting section of the recorded area, and thus it is not possible to maintain good reproduction quality.